Fair Value of Financial Assets and Liabilities - Impact of Valuation Sensitivity (Detail) - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Financial assets:
Trading assets	¥ 6,890,217	¥ 6,176,613
Financial assets at fair value through profit or loss	2,705,113	2,902,969
Financial liabilities:
Financial liabilities designated at fair value through profit or loss	(661,424)	(597,846)
Others	16,425,020	10,346,934
At fair value [member]
Financial assets:
Trading assets	6,890,217	6,176,613
Financial assets at fair value through profit or loss	2,705,113	2,902,969
Investment securities at fair value through other comprehensive income	28,774,141	33,179,136
Financial liabilities:
Financial liabilities designated at fair value through profit or loss	(661,424)	(597,846)
At fair value [member] \| Level 3 [member]
Financial assets:
Trading assets		41,380
Financial assets at fair value through profit or loss	947,153	929,266
Investment securities at fair value through other comprehensive income	678,375	550,448
Financial liabilities:
Financial liabilities designated at fair value through profit or loss	(121,677)	(129,678)
At fair value [member] \| Level 3 [member] \| Financial liabilities at fair value through profit or loss, category [member]
Financial liabilities:
Financial liabilities designated at fair value through profit or loss	(121,677)	(129,678)
At fair value [member] \| Level 3 [member] \| Financial liabilities at fair value through profit or loss, category [member] \| Recorded in profit and loss [member]
Financial liabilities:
Financial liabilities, Favorable changes	228	209
Financial liabilities, Unfavorable changes	244	214
At fair value [member] \| Level 3 [member] \| Others [member]
Financial liabilities:
Others	32,464	14,117
At fair value [member] \| Level 3 [member] \| Others [member] \| Recorded in profit and loss [member]
Financial liabilities:
Financial liabilities, Favorable changes	18	28
Financial liabilities, Unfavorable changes	18	28
At fair value [member] \| Level 3 [member] \| Trading assets [member] \| Debt instruments [member]
Financial assets:
Trading assets		41,380
At fair value [member] \| Level 3 [member] \| Trading assets [member] \| Debt instruments [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes		2,270
Financial assets, Unfavorable changes		2,272
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Interest rate derivatives [member]
Financial assets:
Derivative financial instruments	(7,698)	(4,173)
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Interest rate derivatives [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	12	39
Financial assets, Unfavorable changes	12	39
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Currency derivatives [member]
Financial assets:
Derivative financial instruments	(1,719)	(1,891)
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Currency derivatives [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	2	2
Financial assets, Unfavorable changes	2	2
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Equity derivatives [member]
Financial assets:
Derivative financial instruments	1,583	3,379
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Equity derivatives [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	1,844	1,761
Financial assets, Unfavorable changes	1,811	1,759
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Credit derivatives [member]
Financial assets:
Derivative financial instruments	78	201
At fair value [member] \| Level 3 [member] \| Derivative financial assets [member] \| Credit derivatives [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	16	15
Financial assets, Unfavorable changes	16	14
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through profit or loss [member] \| Debt instruments [member]
Financial assets:
Financial assets at fair value through profit or loss	864,835	849,122
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through profit or loss [member] \| Debt instruments [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	988	724
Financial assets, Unfavorable changes	6,340	1,560
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through profit or loss [member] \| Equity instruments [member]
Financial assets:
Financial assets at fair value through profit or loss	82,318	80,144
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through profit or loss [member] \| Equity instruments [member] \| Recorded in profit and loss [member]
Financial assets:
Financial assets, Favorable changes	125	579
Financial assets, Unfavorable changes	189	682
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through other comprehensive income, category [member] \| Equity instruments [member]
Financial assets:
Investment securities at fair value through other comprehensive income	678,375	550,448
At fair value [member] \| Level 3 [member] \| Financial assets at fair value through other comprehensive income, category [member] \| Equity instruments [member] \| Recorded in equity [member]
Financial assets:
Financial assets, Favorable changes	32,188	19,371
Financial assets, Unfavorable changes	¥ 32,188	¥ 19,371

The amount of decrease in the fair value measurement of assets due to a change in multiple unobservable inputs to reflect reasonably possible alternative assumptions.

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The amount of financial assets at fair value through other comprehensive income. [Refer: At fair value [member]; Financial assets; Other comprehensive income]

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The amount of financial assets at fair value through profit or loss classified as held for trading. A financial asset is classified as held for trading if: (a) it is acquired principally for the purpose of selling it in the near term; (b) on initial recognition it is part of a portfolio of identified financial instruments that are managed together and for which there is evidence of a recent actual pattern of short-term profit-taking; or (c) it is a derivative (except for a derivative that is a financial guarantee contract or a designated and effective hedging instrument). [Refer: At fair value [member]; Financial assets at fair value through profit or loss, mandatorily measured at fair value]

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The amount of financial assets mandatorily measured at fair value through profit or loss in accordance with IFRS 9. [Refer: Financial assets at fair value through profit or loss]

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The amount of financial liabilities that meet either of the following conditions: (a) they meet the definition of held for trading; or (b) upon initial recognition they are designated by the entity as at fair value through profit or loss. An entity may use this designation only when permitted by paragraph 4.3.5 of IFRS 9 (embedded derivatives) or when doing so results in more relevant information, because either: (a) it eliminates or significantly reduces a measurement or recognition inconsistency (sometimes referred to as ‘an accounting mismatch’) that would otherwise arise from measuring assets or liabilities or recognising the gains and losses on them on different bases; or (b) a group of financial liabilities or financial assets and financial liabilities is managed and its performance is evaluated on a fair value basis, in accordance with a documented risk management or investment strategy, and information about the group is provided internally on that basis to the entity’s key management personnel (as defined in IAS 24). [Refer: At fair value [member]; Key management personnel of entity or parent [member]; Derivatives [member]; Financial assets; Financial liabilities]

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The amount of financial liabilities that the entity does not separately disclose in the same statement or note. [Refer: Financial liabilities]

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